Automatic sensitivity reduction system



Nov. 24, 1936. w, VAN B. ROBERTS 2,061,982

AUTOMATIC SENSITIVITY REDUCTION SYSTEM Filed March 30, 1929 jwvemozWALTER VAN .RoERTs Patented Nov. 24,'y 1936 UNITED STATES Y AUTOMATICSENSITIVITY REDUCTION v SYSTEM Walter van B. Roberts, Princeton, N. J.,assignor to Radio Corporation of America, a corporation of DelawareApplication VMarch 30,

8 Claims.

This invention relates to receiver volume control, and, moreparticularly, to the automatic reduction of the sensitivity of areceiving circuit during thetuning of said circuit.

In radio reception, especially in the case of sensitive receivers,thereare present to a great extent, variations in the signal strengthcharacterstics of various broadcasting stations, which render itdiiiicult to obtain satisfactorily uniform reception volume, withouttheuse of special devices to maintain such a uniform volume.

Thus, in tuning a sensitive receiver, through a particular range offrequencies in order to pass fromv one extreme of the range to theopposite extreme, the listener lwill often be subjected to auralannoyance while traversing the frequencies intermediate the saidextremes, it being understood that the intermediate frequencies veryoften include stations emitting powerful signals, or perhaps localstations with comparativelyi strong signal characteristics.

It is possible, o f course, to prevent the raucous and distorted noises,engendered by the traverse over these intermediate channels, by reducingthe amplification of the receiver through manual manipulation of thevolume control mechanism. However, experience has shown that the averageradio broadcast listener regards the repeated resetting of the volumecontrol mechanism as an annoyance, primarily because, when the volume isonce set to his satisfaction, he regards the time taken for readjustmentof the setting as a detraction from the time available for the enjoymentof the broadcast` program.

. Now, I have invented a method of, and means for, eradicating andobviating this source of annoyance to theowner of a broadcast receiver,by providing means vfor insuring automatic reduction of the receivingcircuit sensitivity, and/or amplification, to a point where only apredetermined sound output occurs as the'tuning dial is manipulated pastthe position corresponding to the frequencies of powerful signals.

Briefly, the broad conception embodied in the present invention,involves the uni-control of volume control simultaneously with frequencyselection so that receiver sensitivity is suiciently reduced, atfrequencies of signals, which are abnormally loud in .the particularinstallation, so that only a predetermined sound output occurs whenpassing from one extreme of a predeterminedv range of frequencies to theopposite extreme, and additional means for rendering the abovesensitivity reduction ,control inoperative When desired,

1929, serial NQ. 351,408

(ci. 25o-20) Y The vinvention will be better understood from thefollowing Y description and thel accompanying drawing, in which,

Fig. 1 diagrammatically shows a radio receiver system embodying theprinciples of the invention,

Fig. 2 is a diagrammatic view of the detailsof the automatic sensitivityreduction mechanism,

Fig. 3 is a detailed viewof one ofthe circuit breaker members; and

Fig. 4 shows diagrammatically a modied form of the invention.

Referring to Fig. 1, there is shown a receiver, including a uni-controltuning means, and connectedvvto agrounded antenna circuitMG. The

type of receiver shown herein embodies the well known constructionwherein signal volume is controlled by the introduction of a Variableresistance, the volume of sound from the receiver being increased orreduced by the rotation of an exposed dial,y the dial being connected onthe interior of the setto arheostat which provides the aforesaidresistance.

'This resistance, V, may 'beinserted at any of several points in thereceiver circuit, such as: (1) in the filament circuit oftheradiofrequency amplier tubes, (2) in the plate circuit of the radiofrequency amplier tubes,\(3) in the cathode lead wire common to bothplate and grid circuits. It will be noted that in each casethe volume isreduced when the resistance is increased. All of these constructions andmany others are well known in the art and need not be gone into Vinfurther detailat this point.

r,I 'he radio frequency amplifier is shown as embodying a uni-controltuning means, it being understood that this control is the conventionalone dial gang condenser control. It is understood, of course, that anyother type of tuning means may be employed, the invention depending uponthe mechanical coupling between the tuning means and the volume controlrather than upon the latter two members themselves. The invention asutilized in Fig. 2 embodies two main members comprising one or morenormally short circuited resistances contained in a common circuitrepresented by the letter A in Fig. 1, the common circuit being adaptedto be connected to the receivng circuit, in this case, in series withresistance V. In other words, I insert a number of series connectedresistances in series with the resistance V.

Each of the resistances R, and in Fig. 2 I only show three resistancesR1, R2, R3, is normally short circuited by a spring switch I, 2, 3. Aswitch 9 is Cil shunted across all the resistances, for a purpose to belater described. The circuit A may be so constructed, that it is readilyinserted into a receiving circuit of conventional design, which includesmeans to receive the plugs of the circuit A, it being understood thatslight changes or additions would have to be made in the mechanicaldesign of the receiving circuit.

Each of the switches I, 2, 3 are opened successively by means of aseries of breaker members C, mounted upon a shaft 5. The shaft may bethreaded at one of its endsv for facilitating the attachment thereof tothe interiorly threaded hub I0 of a conventional uni-control tuningshaft.

Fig. 3 shows one of the many possible mechanisms C which may be used asa breaker for each of the switches I, 2, 3, it being understood thatthese mechanisms need not be shaped as shown herein, nor need even becams. Each of the members C is preferably made of a poorly conductingmaterial, such as fiber, hard rubber, etc., and is provided at one endthereof with a hub 'I, whereby the members C may be mounted upon theshaft 5. The hub is bored as at 3, to receive a positioning pin I Iwhereby the members C may be disposed in any predetermined position.

As shown in Fig. 2, each member C is positioned so that each of theswitches I, 2, 3 will be opened by the corresponding breakers C1, C2,C3, the switch I being shown in open position due to the disposition ofthe breaker C1 therebetween.

The operation of the mechanism is readily understood by reference to theabove description, it being understood that as the tuning dial 4rotates, past a given point on the exterior of the set, each of theswitches I, 2, 3 are successively opened by its respective breaker C1,C2, or C3. For example, suppose stations WJ Z and WOR are the twostrongest stations in a given locality, and assume that the operator ofthe receiving set has been listening to station WABC which is a weakstation requiring maximum volume control setting, and it is desired tolisten to station WEAF. (It should be understood that WABC and WEAFrepresent the two extremes of a range of frequencies of which stationsWJZ and WOR are intermediate frequencies.)

If the volume control setting were not disturbed, and my presentinvention were not in use in the receiving circuit, then as the dial 4traversed the angle between the settings of WABC and WEAF, stations WJZand WOR would be heard extremely loud. Consequently, raucous anddistorted sounds would be heard as the dial moved past the positionsrepresenting stations WJZ and WOR.

With my invention, however, as the dial reaches the position wherestation WJZ begins to be heard the breaker C1 moves in between thepoints of switch I and separates them, thereby opening the short circuitaround resistance R1 and effectively inserting more resistance in serieswith resistance V. This results in a reduction of the receiversensitivity at that position, it being understood that the resistance R1is so designed that it adds sufficient resistance to resistance V thatstation WJZ is of a desired loudness. When the dial has passed thefurthest setting where WJZ would be heard, breaker C1 leaves switch Iand R1 is again shortcircuited.

As the dial is rotated still further towards position WEAF the dialposition representing station WOR is reached. As position WOR is reachedthe short circuit around resistance R2 is opened, in a similar fashion,and the, predetermined sound output at this position is not exceeded. Itis understood, of course, that this arrangement is applicable to as manystations as may cause signals which are exceedingly loud when the volumecontrol V is set for maximum. It is also possible to use the samebreaker member C for breaking a series of vertically superposed shortcircuiting switches so that each switch is opened as the breaker membertravels downward or upward through an arc.

In case it is known that a broadcasting station emitting weak signals,for the particular locality in which reception is being employed,possesses the same Wave length as one of the strong stations alreadyreferred to, and it is desired to receive this weak station when thelocally strong station is not transmitting, I provide a master switch 9.This switch allows the receiver to operate on all wavelengths with themaximum sensitiveness determined by the setting of the volume control V.

In other words, the switch 9 renders the auxiliary volume control Ainoperative when desired. Various manually operable switches may also beemployed to restore maximum sensitivity at the frequency of any one ormore intermediate stations, while maintaining reduced sensitivity atother angular positions of the tuning dial.

For example, each of the resistances R1, R2, Rf1 may be provided with asmall manually operable 'short circuiting switch which may be shunted oaround each resistance. As stated heretofore, it is not essential tothis invention that the main volume control V be inserted at anyparticular part of the circuit, for the broad concept of the invention,which is illustrated by the drawing, involves the method of maintaininga low sensitivity in a receiving circuit over certain predeterminednarrow bands of frequencies, which consists in reducing the circuitsensitivity through a predetermined narrow range of frequenciessimultaneously` with the tuning of the circuit to said frequencies.

It Should be noted that in some cases the volume control resistance maybe so located in the receiver circuit that volume is reduced byincreasing the control resistance. An example yof this is shown in Fig.4 where a resistance is inserted between antenna and ground. In such acase switches I, 2' and 3 connect R1, R2, and R3 respectively, inparallel with the volume control resistance V' when operated by the camsCi, C2, C3. The master switch 9 is opened in this case to restore normalsensitivity at all frequencies.4 The switches I', 2 and 3 are normallymaintained open by springs I5.

It will be obvious that the general principles herein disclosed may beembodied in many organizations and constructions widely different fromthose illustrated herein without departure from the spirit of theinvention as defined in the following claims.

What I claim is:

1 In a radio receiving set of the uni-control tuning type, including avariable resistance for controlling signal Volume, means including aplurality of normally short-circuited resistances in series, adapted tobe connected to said Variable resistance, and means, operativesimultaneously with the uni-control tuning means, for successivelybreaking the short circuits within predevfrequencies in the said range.

3. In a tunable amplifier of the type provided with a continuouslyvariable signal energy selecting means, a Signal Volume control meansincluding a Variable resistor device, a plurality of normallydisconnected auxiliary resistance elements and means for connecting saidresistance elements to said variable resistor device in a predeterminedsequence to produce additional volume controlling effects upon saidamplifier, said last named means being simultaneously operative withsaid signal energy selecting means.

4. In the operation of radio receiving apparatus having one or morecircuits tunable by adjustment ofthe movable elements of tuning devicesassociated therewith, the method which comprises moving said elementscontinuously to change the resonant frequency of said circuits in searchof signals from a. desired station, and utilizing the movementtemporarily to depress the sensitivity of the apparatus as the resonantfrequency of thecircuits passes through transmission frequency of nearbyor powerful stations.

tus having means to adjust sensitivity and one f or more circuitstunable by adjustment of the tus having one or more circuits tunable byadjustment of the movable elements of tuning devices associatedtherewith, and impedance controlling the amplitude of reproducedsignals, the method lwhich comprises moving said elements continuouslyto change the resonant frequency of said circuits in search of signalsfrom a desired station, and utilizing the movement to effect temporarychange in the effective magnitude of said impedance as the resonantfrequency of the circuits passes through the frequency df' transmissionfrom nearby or powerful stations, in a sense reducing the amplitude ofsignals therefrom. n

'7. Radio receiving apparatus comprising thermionic tubes, circuitsincluding tuning devices having elements adjustable to tune saidcircuits to all frequencies Within a range of. frequencies,

a calibrated operating dial therefor, an imped-V ance adapted to controlthe sensitivity of said apparatus, and means movable in unison with saidadjustable elements throughout their range of movement varying theeffective magnitude of said impedance in a sense to depress sensitivitywhen said dial is at a setting corresponding to the frequency oftransmission from a powerful station.

8. In the operation of radio receiving apparatus having one or morecircuits tunable by adjustment of the movable elements of. tuningdevices associated therewith and volume control means, the method whichcomprises moving said elements to continuously change the resonantfrequency of said circuits from one point within a range of frequenciesto another point. thereof in search of signals from a desiredtransmitting station and utilizing the movement temporarily to operatethe volume controlling means so as to maintain the receiving apparatusoutput substantially constant as the resonant frequency of the circuitspasses through certain predetermined values.

WALTER VAN B. ROBERTS.

